The Uptake of Phosphorus by Bean Plants with Particular Reference to the Effects of Iron.

This paper presents some of the findings of a study of the uptake of phosphorus by bean plants as it is influenced by iron. As a result of this work a number of points have been brought out which have not been clearly stated previously. In order to complete the study successfully, the effects of pH and the simultaneous effects of various phosphorus and iron supplies were considered. The results show: (a) Absorbed iron ties up a portion of the " seed phosphorus " in an unusable condition. (b) A ferric phosphate precipitate, in or on the roots, retards the flow of phosphorus to the actively growing leaves. (c) As the phosphorus content of the nutrient medium is increased, roots, stems, and cordate leaves continue to build up in phosphorus content even after trifoliate leaves are being adequately supplied. The excess phosphorus may be responsible for immobilizing iron and other ions. The effect of the hydrogen ion concentration on the absorption of phosphorus by higher plants was studied by ARNON et al. (2) as part of a more comprehensive investigation of the absorption of inorganic nutrients. They showed that the amount of phosphate absorbed varied both with the plant and also with the pH of the nutrient solution. With tomato, maximum absorption occurred at pH 7, decreasing toward pH 3 and pH 9. With Bermuda grass there was no marked variation in the phosphorus absorption between pH 4 and pH 7, although a tendency toward a minimum appeared at pH 6. At a pH of 3 and pH 9, which are extremes under which plants barely persist, the phosphorus absorption was much lower. Because of this variation between plants, a study was undertaken of the absorption of phosphorus by bean plants grown in water cultures maintained at various pH values. The effect of iron on the absorption of phosphorus has not been studied directly. However, relationships between the two have been reported by a number of workers. AIYAR (1), using solution cultures, found that increasing concentrations of phosphorus caused an increase in the phosphorus content of the roots, but a decrease in the nitrogen and iron contents. THONIAS